If the trailer begins to sway or fishtail behind you, what is a key part of the correct response?

Correct answer to question 364 (General Knowledge): Ease off the accelerator gradually rather than braking hard or steering sharply

Why

Hard braking or sharp steering while a trailer is swaying can make the sway worse or trigger a jackknife, so gradually easing off the throttle to let the trailer settle is the safer response.